[loveforfish]

im a beginer to marine tanks but want to try a small 20 gallon reef with a few small fish.. what should i look into

[mbunakeith]

research, research and more research. this is a good start.
i finally setup my 20g nano reef a couple years ago after keeping freshwater tanks for years. i did a lot of research, built a tank with overflow, sump, scwd (wavemaker), mh lighting the whole thing. it worked beautifully, but it was very time consuming. i am not trying to scare you away or anything, but just to warn you about small tanks. small tanks change quickly. if you have any sort of problem it will happen fast. if your topoff system overflows on a small system it only takes a matter of seconds to become a freshwater system. if your calcium is difficult to control you can have wild ph and alk swings.
what i recommend is to get a good idea of what kind of corals you want in your tank and work around that idea. if you have a 20g tank, you can realistically only have two very small fish in there for any true success. i would plan the fish around the corals. for example, you arent going to want a sand sifting goby if you have a bunch of plate corals or brains because the fish will spit sand on them all the time.
i would recommend as large a sump as you can get for the tank. this will help you in many ways. you can hide your heaters in it, you can put cheatomorpha in it to eat up extra nutirients, it will add more water volume to add stability and make it easier to make chemical changes to your system or make it a dsb (deep sand bed) for nitrate & nutriet consumption.
i had an auto-topoff system in my sump that elliminated having to top off the tank every day. you can also hide your big skimmer in the sump too. this is just to start with. if you have any more questions ask away, that is what we are all here for.
also, red sea makes a pretty neat all-included tank now that seems really nice. i would plumb it for a sump though.